1. Field of the Invention
The present invention relates to an electret transducer, and more particularly, to an electret transducer powered by solar energy.
2. Description of the Related Art
An electroacoustic loudspeaker is a transducer converting electric energy to sound energy. The transducers can be categorized into three types by the way in which they are driven. The three types of transducers are as follows: moving-coil transducer, piezoelectric transducer, and electrostatic transducer.
Currently, the moving-coil transducer is the most commonly used transducer and has been widely applied to products such as TVs, radios, earphones and cell phones. However, the development of the moving-coil transducer is limited by the inherent structure and the inflexible design in electric energy, thus, the moving-coil transducer is unable to meet the requirements of portable and low current-consuming electronic products. Additionally, the traditional electrostatic transducer requires a high DC bias (about 1500 volt to 2000 volt) amplifier which incurs high cost, thus it is not suitable for portable products. Therefore, a need exists in the art for an energy efficient, compact and transparent electroacoustic transducer with high reproduction quality.
Due to its flexible feature, the electret transducer is also called soft loudspeaker. The electret transducer features compact form, high efficiency, large bandwidth and less distortion and is of great potential to be applied in portable products when product volume and efficiency are taken into consideration.
In another aspect, when designing portable 3C products, one should pay as much attention to the source of the power supply as s/he does to the volume of the products. As shown in FIG. 1, in an amplifier circuit 10 of the traditional transducer, a DC power source 14 is supplied to an audio amplifier 12 to boost the voltage of an audio signal so as to vibrate a thin film of a loudspeaker 16 to generate a sound.
Presently, great efforts have been made by people from all walks of life to find an environmental friendly and sustainable electric energy source, thus, technologies using solar cells as power supply source are booming. Solar power is not only renewable, but also has the potential to be applied to portable products. Please refer to FIG. 2, it shows an amplifier circuit 20 of the traditional transducer in which a solar cell 24 is used as a DC power source to drive an audio amplifier 22. As the audio amplifier 22 of the traditional transducer requires high DC bias, it remains a need to integrate the solar cell 24 with a charging circuit and an energy-storage cell 25. The solar cell 24 charges the energy-storage cell 25 through the charging circuit so as to further provide power to the audio amplifier 22 to boost the voltage of an audio signal, thereby vibrating a thin film of a loudspeaker 26 to generate a sound.
As described above, the present systems using solar energy as power source need to be integrated with charging circuits and energy-storage cells to charge and store energy. Currently, there are no transducers operable without having to store electric energy.